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Process Control & Automation Flashcards

7 cards from real CPT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Process Control & Automation flashcards as text

  1. In a cascade control system, which controller receives the setpoint from the operator?

    Answer: Primary (master) controller

    In cascade control, the operator sets the setpoint on the primary controller, which then outputs a setpoint to the secondary controller.

  2. What does the term 'offset' refer to in a proportional-only control loop?

    Answer: A sustained steady-state error between setpoint and process variable

    Proportional-only control produces a permanent offset (steady-state error) because it cannot eliminate error without integral action.

  3. Which valve characteristic provides an equal percentage change in flow for equal increments of valve travel?

    Answer: Equal percentage

    Equal percentage valves produce a constant percentage change in flow per unit of stem travel, making them suitable for processes with variable pressure drops.

  4. A control valve with an air-to-open (ATO) actuator will fail in which position on loss of instrument air?

    Answer: Closed

    An air-to-open valve requires air pressure to open; when air is lost, the spring returns the valve to the closed (fail-closed) position.

  5. What is the function of a positioner on a control valve?

    Answer: To ensure the valve stem reaches and maintains the position commanded by the controller output

    A valve positioner uses feedback from the stem position to ensure the valve accurately follows the controller output signal, overcoming friction and hysteresis.

  6. In process control, what is 'integral windup' and when does it occur?

    Answer: Accumulation of integral action while the controller output is saturated

    Integral windup occurs when the controller output saturates (hits a limit) and the integral term continues to accumulate error, causing delayed response when the process returns to normal.

  7. Which control strategy is best suited for compensating for measurable disturbances before they affect the process variable?

    Answer: Feed-forward control

    Feed-forward control measures a disturbance and applies a corrective action before the disturbance affects the controlled variable, unlike feedback which reacts after the fact.